1. Field
The subject invention is in the field of extendable/retractable apparatus such as tent poles, fishing rods and boat hooks which can be set at any length within a length range. More specifically it is in the field of such apparatus which incorporates mechanism by which one mechanism at one end of the apparatus operates and controls another mechanism at the other end of the apparatus. Still more specifically it is in the field of such apparatus and related mechanisms adapted for use with apparatus used in construction of dry walls in buildings, apparatus known in the trade as a flat finishing box, used in the crowning and finishing of taped joints between drywall panels.
2. Prior Art
Known prior art is shown in the patents listed below. These patents are:
In the field of drywall construction and finishing, apparatus termed a flat finishing box is attached to a handle to enable the operator to apply the box to the joints being serviced by the box. To adapt the apparatus to various use situations various lengths of handles are needed to work with, for example, a variety of heights of ceilings and, also, the box must be set in a range of angles with respect to the long axis of the handle. The conventional apparatus comprises a fixed length handle with a lever at one end operable to lock the box pivoted at the other end of the handle at a specific angle in a range of angles to the handle axis. When a variety of lengths of handles is required, it is necessary either to have a number of flat finishing boxes, each attached to a specific length handle or to use fewer boxes than handle lengths required, (usually one box) and interchange the box or boxes from handle to handle in order to have the box on a handle of suitable length. The use of multiple boxes, each with a different length handle attached, is not generally acceptable because of the cost and because the compound used in the boxes sets up, i.e. hardens, so that compound in boxes not fully emptied in use is wasted and removal of the wasted compound is time consuming. The use of fewer boxes than handles is standard practice but changing the boxes from handle to handle is time consuming and tends to be awkward if the box contains the compound referred to in the trade as xe2x80x9cmudxe2x80x9d.
Therefore, for flat finishing drywall joints more efficiently in terms of the interrelated factors of time and cost, there has been a need for a flat finishing tool with an adjustable length handle, particularly one adjustable to specific lengths in a range of lengths.
U.S. Pat. No. 5,099,539 (Forrester), U.S. Pat. No. 5,088,147 (MacMillan, the inventor of the subject invention) U.S. patent application, Ser. No. 09/414,677 by MacMillan and U.S. patent application, Ser. No. 09/502,896, also by MacMillan all show adjustable length handles for flat finishers. All of these handles have a lever pivoted at one end and a part called a box footplate pivoted at the other. In use a flat finishing box is attached to the footplate, the handle is adjusted to the needed length and the handle is maneuvered to place the box against the work surface. This placement sets the box and box footplate at an angle to the long axis of the handle and the lever is operated to lock the box and box footplate at that angle relative to the handle. The mechanical complexity of these prior art adjustable length handles for flat finishers is typical in the prior art and increases first and maintenance costs of the handles and degrades their reliability, thereby increasing operation costs. The lock mechanism in particular tends to be delicate relative to its performance requirements and the range of angular motion of the box footplate is quite limited. The handle of U.S. patent application, Ser. No. 09/414,677 is considered to be the least complicated and most rugged of the three prior art handles. Nevertheless, there is a continued need for more ruggedness and simplicity, to reduce first, use and maintenance costs.
Accordingly, the primary objective of the subject invention is to provide a less complicated adjustable length handle for flat finishers because of the significant savings in costs that the reduced complication facilitates. Other objectives are that the range of angular motion of the box footplate be relatively large, that there be no highly loaded small parts, that the handle be relatively lightweight and that it be ergonomically acceptable.
The subject invention is an adjustable length handle for flat finishers. The primary structural components of the handle are two telescopic tubes. Relative rotation of the engaged tubes is prevented by engagement of a longitudinal rib on the outside of one tube with a groove in a fitting on the other tube. When the tubes are telescopically engaged each has an overlapped end and a free end. A fitting termed a box footplate is pivotally attached to a second fitting attached to the free end of the larger, outer tube, with a pivot axis perpendicular to the long axis of the tubes. The rotation of the footplate with respect to the long axis of the tubes is controlled by a connecting link which connects the footplate to a tube which is slidably mounted in the handle with its axis parallel to the axis of the handle. A lever pivoted at the free end of the smaller tube is linked to a clamp mechanism anchored in the overlapped end of the smaller tube. The tube linked to the footplate extends through and is supported by the clamp mechanism. Operations of the level clamps the linked tube, preventing it from linear motion and thus preventing rotation of the footplate relative to the handle.
The clamp mechanism comprises three parts: a base, a clamp and a clamp actuator. The base is attached inside the overlapped end of the smaller tube. The clamp is installed in the base and fastened in it so that it cannot move endwise. There is a hole endwise through the clamp for tube which is linked to the footplate and a slit from the hole to the upper face of the clamp. Pressure to narrow the slit clamps the tube. Pressure is applied by longitudinal motion of the clamp actuator. A cam follower roller on the clamp engages a slanted slot in the actuator so that longitudinal motion of the actuator causes lateral motion of the cam follower and the portion of the clamp it""s attached to.
The invention is described in more detail below with reference to the attached drawings.